One of the ways to control the spatial distribution of an optical beam, such as a laser beam or a beam of light from one or more light emitting diodes (LEDs), is to use a diffractive diffuser. Unlike conventional optical components such as refractive lenses and prisms, which control the spatial distribution of light primarily by means of refraction of light at the surfaces of dielectric media, diffractive diffusers control the spatial distribution of light by means of diffraction.
While there are many applications in which diffractive diffusers have been found to be useful, limitations of the existing technology prevent the expansion of the uses of diffractive diffusers into additional areas of application. Among these limitations are (1) the lack of the ability to electronically switch the characteristics of diffractive diffusers, (2) an upper limit on the angular range through which light can be diffracted using available types of diffusers, and (3) excessive fabrication time and cost.
The limitation of currently available diffractive diffusers on the capability to allow electronic switching of optical properties is inherent in the material structure of these diffractive diffusers. Currently, diffractive diffusers are static dielectric structures that are only minimally affected by the application of an electric field. Therefore, the optical properties of diffractive diffusers based on prior art cannot be electronically switched to any meaningful extent.
The limitation of currently available diffractive diffusers on the angular range through which light can be diffracted is due to the inability to achieve sufficiently fine feature sizes. The range of diffraction angles of which a diffractive diffuser is capable is inversely proportional to the minimum feature size of said diffractive diffuser. More specifically, the maximum angle in radians through which a diffractive diffuser is capable of diffracting a light beam is approximately the wavelength of the light divided by the minimum feature size.
An additional limitation of the existing technology is that the processes for fabricating a custom diffractive diffuser are time-consuming and expensive. Typically, the processes required to produce a diffractive diffuser include multi-step photolithography and various types of etching, such as reactive ion etching or acid etching.
The technology of diffractive waveplates, including electronically switchable diffractive waveplates, has been applied to several areas of optics, allowing, for example, lenses whose focal lengths are electrically switchable, and beam deflectors that can be switched on and off. However, diffractive waveplate technology has not been applied to design and fabrication of diffractive diffusers, and in particular, it has not been applied to fabrication of electronically switchable diffractive diffusers, i.e. diffusers whose diffractive properties can be electronically switched on and off.
Thus, there is a need for beam shaping systems with electronically switchable characteristics, with feature sizes smaller than are readily attainable with existing technology, and for which the associated fabrication technology does not involve time-consuming or expensive processes.